The present invention relates to magnetic tape cassettes. More particularly, the invention relates to a so-called Phillips-type magnetic tape cassette in which a magnetic tape wound on a pair of winding cores is loaded between the upper and lower halves of the cassette.
Heretofore, in a magnetic tape cassette of this type, the space defined by the upper and lower halves is divided in an area ratio of the order of 5:1 into a winding core accommodating region for accommodating the winding cores and a recording and reproducing region by partition members which form a single partition along the front opening of the cassette.
In addition, rotary guide rollers which contact the base side of the tape to guide the running of the tape are arranged at both ends of the recording and reproducing region, which occupies the front part of the cassette. When the tape is run while contacting the outer walls of the rotary guide rollers with a predetermined angle, the rotary guide rollers are turned in the tape running direction so as to smoothly change the tape running direction in the recording and reproducing region and the winding core accommodating region. Accordingly, the tape running characteristic in the recording and reproducing region is greatly affected by the characteristics of rotation of the rotary guide roller.
The fundamental structure of the above-described conventional guide roller will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view of the cassette showing the rotary guide roller.
As shown in FIG. 1, each rotary guide roller 2 is mounted on a supporting shaft 8 which extends from a mounting seat 7 in the lower half 6 of the cassette. The rotary guide rollers 2 are rotatably arranged on both sides of a recording and reproducing region A which occupies the front part of the cassette 1. The upper half 9 has a mounting seat 10 having a recess 11 which receives the supporting shaft 8. Because the end portion of the shaft 8 is inserted into the recess 11, the vertical movement of the guide roller 2 is limited by the mounting seats 7 and 10.
A magnetic tape T is laid over the rotary guide rollers 2 in such a manner that its base side is in contact with the cylindrical outer wall 3 of each roller 2 with an angle formed by the tape running direction in the recording and reproducing region A and the winding core accommodating region B. As the tape T runs, the guide roller 2 is rotated in the tape running direction to guide the tape T.
The guide roller 2 has flanges 4 at both ends to prevent the vertical displacement of the tape T from the cylindrical outer wall 3. However, since there are small gaps between the mounting seats 7 and 10 and the two end faces of the guide roller 2, respectively, the guide roller 2 is allowed to move up and down in the direction of the axis of the supporting shaft 8. That is, although the guide roller 2 has the flanges 4, the tape still can move somewhat in its widthwise direction. For the same reason, when shock or vibration is imparted to the cassette 1 from the outside, the guide roller 2 is caused to move up and down, thus causing the tape T to be displaced in its widthwise direction.
In general, the upper and lower halves 6 and 9 of the cassette are made of a plastic resin. Therefore, it is difficult to dsign the upper and lower halves so that, when they are combined together, the aforementioned gaps are very small. On the other hand, in order to provide smooth rotation of the guide roller, there must be suitable gaps between the mounting seats and the two end faces of the guide roller.
Heretofore, in recording or reproducing signals with the cassette 1, the number of tracks has typically been four. Accordingly, the displacement of the tape T in its widthwise direction, being small compared with the track width, causes no tracking error.
There has been a strong demand for the provision of a cassette suitable for recording and reproducing signals with a high density for multi-track recording. For instance, in a pulse code modulation (PCM) type signal recording and reproducing system for a digital audio system, multiple tracks, for instance thirty-two tracks, are used for recording and reproducing signals with the conventional Phillips-type cassette. In this case, the width of each track is of the order of 100 microns, which is considerably smaller than the conventional track width. Accordingly, even a slight shift of the tape T in its widthwise direction causes a tracking error.